Influence of bolt tightening torque,wire size,and component reuse on wire fixation in circular external fixation

OBJECTIVES: To evaluate the effects of bolt torque, wire size, and component reuse on the ability to maintain wire tension in 3 external skeletal fixation systems. STUDY DESIGN: Biomechanical study. METHODS: Yield strength in tension of 1.0-, 1.2-, 1.5-, and 1.6-mm-diameter wires, and yield strength in torque of Hofmann Small Bone Fixation (SBF) cannulated and slotted bolts and IMEX regular and miniature bolts were determined on a testing machine. The minimum bolt tightening torque needed to prevent wire slippage at clinically recommended wire tensions was determined. Components were tested 10 times, and loads at slippage were recorded. RESULTS: The IMEX system required a mean of 8 Nm of bolt tightening torque to maintain 900 N (1.6-mm wires). The SBF system required a mean of 3 Nm bolt torque to maintain 300 N (1.0-mm wires) and 5 Nm to maintain 600 N (1.2-mm wires). The SBF cannulated bolt required 9 Nm of torque to maintain 900 N (1.5-mm wires). The SBF slotted bolts could only maintain 800 N before yield. The IMEX miniature system required a mean bolt torque of 1.1 Nm to maintain 300 N. The cannulated and slotted bolts from both manufacturers failed to maintain 70% of initial wire tension after 7 and 4 uses, respectively. CONCLUSIONS: The IMEX systems and the SBF system using 1.0- and 1.2-mm wires could maintain clinically recommended wire tension safely. Only the IMEX system could maintain clinically recommended wire tension safely using 1.5- or 1.6-mm wires. CLINICAL RELEVANCE: The SBF system using 1.0- and 1.2-mm wires and the IMEX system using all wire sizes can maintain clinically relevant wire tension. The SBF system using 1.5-mm wires could not. Cannulated and slotted bolts should not be used more than 6 and 3 times, respectively. Nuts should not be reused.     

Static and Dynamic Cerclage Wire Analysis

A new type of double loop cerclage wire, conventional single wire loop cerclage, and twist-type cerclage were evaluated. The double loop cerclage was applied using the Osteo Systems double loop tightener. Two groups of single wire loop cerclage were applied using the Osteo System loop tightener and the Richards loop tightener. Two groups of twist-type cerclage were applied using the Kirschner wire twister and side-cutting pliers. The test system allowed determination of the static tension produced by each wire, as weH as its ability to resist distraction. The double loop cerclage wires were the most effective in producing static tension and in resisting distraction. While the conventional single loop cerclage wires produced more static tension than the twist cerclage wires, they were less effective in resisting distraction.     

Evaluation of four interfragmentary Kirschner wire configurations as a component of screw/wire/polymethylmethacrylate fixation for acetabular fractures in dogs

The biomechanical contribution of the interfragmentary Kirschner wire as a component of composite fixation for acetabular fracture repair was subjectively and objectively evaluated. Acetabular osteotomies were repaired using the screw/wire/polymethylmethacrylate (SWP) composite fixation with or without one of three configurations of Kirschner wire in 32 hemipelves obtained from 16 dogs. Reduction, assessed objectively and subjectively, was unaffected by Kirschner wire placement. Hemipelves repaired with Kirschner wire(s) were subjectively more stable prior to application of polymethylmethacrylate when manually assessed in multiple planes. Consistent incremental increases in stiffness, yield load, and maximum load sustained that were observed during biomechanical testing were not significant, with the exception that hemipelves repaired with two Kirschner wires had significantly greater yield loads than hemipelves repaired without Kirschner wires. The subjective results of this study support the use of at least one interfragmentary Kirschner wire to maintain reduction prior to polymethylmethacrylate application; however, fracture configuration and location may dictate the number and pattern of interfragmentary Kirschner wires used to maintain reduction prior to application of the polymethylmethacrylate. The objective results and observations made during biomechanical testing suggest that use of one or more interfragmentary Kirschner wires may enhance stability after polymethylmethacrylate application.     

Comparison of Alternate and Simultaneous Tensioning of Wires in a Single-Ring Fixator Construct

Objective— To measure and compare the strain of wires tensioned with alternate (ALT) and simultaneous (SIM) tensioning in a single-ring fixator construct and compare the stiffness of these constructs under axial loading.
Study Design— Experimental mechanical study.
Sample Population— Twenty-four, 84 mm diameter, single-ring constructs.
Methods— Twenty-four, 84 mm diameter, single-ring constructs were assembled using 2 1.6 mm wires placed at a 60° angle tensioned with either ALT or SIM technique to 90 kg tension. Voltage data from a strain gauge were recorded during the wire-tensioning process, cyclic axial loading, and load-to-failure testing. Wire strains were calculated for each wire and compared within constructs and between ALT and SIM groups. Construct stiffness was compared between groups.
Results— There was no difference between the tensioning methods in final wire strains after initial tensioning for both the wire below the ring (W1; P =.698) and the wire above the ring (W2; P =.233). There was also no difference in final wire strains within each tensioning method group (ALT, P =.289; SIM, P =.583). Loss of wire strain (3.5–5%) occurred after cyclic loading for both wires in both groups. There was no difference in construct stiffness between the ALT and SIM groups ( P =.126). Mode of failure was by wire breakage in all constructs and occurred most frequently in W1.
Conclusion— ALT tensioning of wires produced similar wire strains within a single-ring construct after initial tensioning to SIM tensioned wires. There was no difference in construct stiffness under axial loading between AIM and SIM tensioned constructs.
Clinical Relevance— ALT tensioning of wires in a single-ring fixator construct can be used as an alternative to SIM tensioning, as similar initial wire tensions are achieved.     

Effect of Cerclage Wires on Periosteal Bone in Growing Dogs

Three diameters of wire were placed circumferentially around the femora of six 22 week old puppies. The wires were placed over the periosteum on one limb and under the periosteum on the other limb. The effect of the wires on actively growing bone was evaluated 3 and 8 weeks after placement. Diffuse growth of periosteal new bone occurred in immature dog femora in which cerclage were placed under the periosteum. This reaction corresponded with dramatically increased medullary and periosteal microvascularity coupled with histologic active trabecular bone formation. In femora in which wires were placed over the periosteum, even though the placement of the wires should supposedly have been the most detrimental, there were active vessels within the cortex directly under all wires. In both preparations, cerclage wires were becoming encased in the growing cortical bone 8 weeks after placement. Cerclage wires did not devitalize immature bone nor did it restrict adjacent appositional bone growth.     

Resistance of cerclage to knot failure

The comparative ability of loop-knotted and twist-knotted cerclage to withstand tensile forces was tested. Two twist-knot devices and one loop-knot device were used to apply cerclage wires to a 5-cm diameter split circular jaw mounted on a tensile testing machine. Twist-knot devices were tested with 0.8-, 1.0-, or 1.2-mm wire, and the loop-knot device was tested with 0.8-, 1.0-, or 1.25-mm wire. For all wire sizes, the twisted knot provided greater resistance to knot failure than did the loop-knot. Of the 2 twist-knot devices, the Rhinelander wire tightener-twister produced the greatest resistance to knot failure. Knot resistance increased with increase in wire size for all devices tested.     

Effects of ring diameter and wire tension on the axial biomechanics of four-ring circular external skeletal fixator constructs.

OBJECTIVE: To determine relative effects of ring diameter and wire tension on axial biomechanical properties of 4-ring circular external skeletal fixator constructs. SAMPLE POPULATION: 4-ring circular external skeletal fixator constructs and artificial bone models. PROCEDURE: 4-ring constructs were assembled, using 50-, 66-, 84-, or 118-mm-diameter rings. Two 1.6-mm-diameter fixation wires were attached to opposing surfaces of each ring at intersection angles of 90 degrees and placed through a gap-fracture bone model. Three examples of each construct were loaded in axial compression at 7 N/s to a maximum load of 400 N at each of 4 wire tensions (0, 30, 60, and 90 kg). Response variables were determined from resulting load-displacement curves (construct stiffness, load at 1 mm of displacement, displacement at 400 N). RESULTS: Ring diameter and wire tension had a significant effect on all response variables and had a significant interaction for construct stiffness and displacement at 400 N. Significant differences within all response variables were seen among all 4 ring diameters and all 4 wire tensions. As ring diameter increased, effect of increasing wire tension on gap stiffness and gap displacement at 400 N decreased. Ring diameter had a greater effect than wire tension on all response variables. CONCLUSIONS AND CLINICAL RELEVANCE: Although effects of wire tension decrease as ring diameter increases, placing tension on wires in larger ring constructs is important because these constructs are inherently less stiff. The differential contribution of ring diameter, wire tension, and their interactions must be considered when using circular external skeletal fixators.     

Splenic abscesses due to migrant metallic wires from small intestine in a horse

This reports discusses a perforating metallic wire that was suspected of causing chronic weight loss, inappetance and pyrexia in a 15‐year‐old Standardbred gelding, due to the fact that during the previous 18 months, 6 horses coming from the same yard were referred for recurrent or acute colic related to the ingestion of metallic wires. Splenomegaly was detected ultrasonographically and confirmed during surgery. During necropsy, 2 metallic wires 0.2 mm in diameter and 3–4 cm long were found in a markedly enlarged spleen with several nonencapsulated abscesses. Metallic wire perforation and migration through the lower alimentary tract may involve different abdominal quadrants (intestine, abdominal wall, spleen, liver) and lead to different clinical syndromes as acute or recurrent colic and weight loss. A clinical diagnosis is challenging as the clinical signs are often nonspecific and prognosis is generally considered poor.     

Mechanical Characteristics and Comparisons of Cerclage Wires: Introduction of the Double-Wrap and Loop/Twist Tying Methods

Objective — Evaluate the mechanical properties of twist, loop, double loop, double-wrap and loop/twist cerclage.
Methods — The initial tension generated by 18 cerclage of each type was determined using a materials testing machine after tying around a testing jig. Six wires from each type were distracted and the initial stiffness and yield load were determined. Yield behavior was further investigated in six wires of each type by determining the load required to reduce cerclage tension below 30 Newton (N) following an incremental (50 N) stepwise load and unload regimen. The amount of collapse of the simulated bone fragments that resulted in the reduction of initial tension to 30 N was measured for the final six wires of each group. Data were analyzed by analysis of variance and a multiple comparison test.
Results — Twist type cerclage generated less tension than loop-type cerclage. The yield load of these two types was similar. Double-loop and double-wrap cerclage generated superior tension and resisted a greater load before loosening. Loop/twist cerclage had an intermediate initial tension but had the greatest resistance to loading. In the collapse test, the greater the initial tension, the more collapse could occur before the wire was loose. For all types of cerclage wire fixation, a reduction of diameter of the testing jig of more than 1% caused loosening.
Clinical Relevance — Double-loop and double-wrap cerclage provide greater compression of fragments and resist loads associated with weight-bearing better than the twist and loop methods. Loop/twist cerclage may have advantages because of their superior resistance to loading. All cerclage will loosen if fracture fragments collapse.     

Axial Characteristics of Circular External Skeletal Fixator Single Ring Constructs

OBJECTIVE: Evaluate the effects of varying ring diameter, wire tension, and wire-divergence angle on the axial stiffness characteristics of circular external skeletal fixator single-ring constructs. Study Design-Biomechanical evaluation using circular fixator components and a Delrin cylinder bone model. METHODS: Single ring constructs using two 1.6 mm diameter Kirschner wires to secure a 19 mm Delrin cylinder centered within the ring were examined. Component variables evaluated were ring diameter (50 mm, 66 mm, 84 mm, and 118 mm), wire-divergence angle (30 degrees, 60 degrees, and 90 degrees ), and wire tension (0 kg, 30 kg, 60 kg, and 90 kg). A total of 48 constructs were examined. Rings were rigidly mounted on a universal testing system and the cylinder loaded in axial compression (7.4 N/s) to 220 N. Load/displacement curves were analyzed to determine the following: the displacement (mm) that occurred before the slope of each load/displacement curve became linear, the stiffness (N/mm) of the linear portion of each load/deformation curve, and the total displacement (mm) produced at maximal load. Least-squares linear regression was used to model response variables as linear functions of ring diameter, wire divergence angle, and wire tension. Three-way interactions and 2-way interactions among independent component variables were evaluated first in the modeling process and included in a best model if response variables were found to have statistically significant regression coefficients. The regression coefficients and corresponding standard errors and covariances were used to estimate the maximal effect and standard error attributable to wire divergency angle (change from 30 degrees to 90 degrees ) and wire tension (change from 0 to 90 kg) for each ring diameter. RESULTS: All load/deformation curves had an initial exponential increase in stiffness, with the slope becoming linear at higher loads. The exponential phase was more pronounced in larger-diameter ring constructs and was mitigated by tensioning the wires. Ring diameter had the greatest influence on displacement that occurred before the curve became linear (semipartial r(2) [sp-r2] = .89), stiffness (sp-r2 = .94), and total displacement (sp-r2 = .93). Wire tension exerted a smaller influence on displacement that occurred before the curve became linear (sp-r2 =.06), stiffness (sp-r2 = .03), and total displacement (sp-r2 = .05). Wire divergence angle had a nominal effect on displacement that occurred before the curve became linear (sp-r2 = .0001), on stiffness (sp-r2 = .004), and on total displacement (sp-r2 =.003). CONCLUSIONS: Ring diameter had a profound effect on the axial stiffness characteristic of single ring constructs. Tensioning of the fixation wires can improve the axial stiffness characteristics of these constructs, particularly in larger diameter ring constructs, by mitigating the initial exponential phase of the load/deformation curve. Wire divergence angle had only a nominal differential effect on axial stability. CLINICAL RELEVANCE: Understanding how individual component variables and their interactions influence bone segment stability should help surgeons to optimize interfragmentary strain. Tensioning fixation wires is probably unnecessary in 50 mm diameter ring constructs, but assumes greater importance as ring diameter increases.     

Evaluation of tension obtained by use of three knots for tying cerclage wires by surgeons of various abilities and experience

OBJECTIVE: To compare tension of 3 cerclage wire knots tied by surgeons of various abilities and experience. DESIGN: Cross-sectional study. SAMPLE POPULATION: Participants and faculty at a postgraduate course in veterinary orthopedics. PROCEDURE: Subjects tied a cerclage of their choice on an instrumented tying stand that displayed the tension on a computer. Mean tensions in cerclage wires tied with twist, single loop, or double loop knots were compared. The relationship between level of surgeon experience and tension achieved was examined. RESULTS: 29 twist, 30 single loop, and 16 double loop wires were analyzed. Mean +/- SD tension for twist knots was significantly less than for single loop knots (82.3+/-46.1 vs 166.6+/-42.2 N, respectively). Double loop knots achieved significantly greater tension (392.0+/-116.6 N) than twist and single loop knots did, even though few participants had ever tied this knot previously. There was no correlation with experience of the participant. For twist knots, wiggling the wire during cutting and pushing the twist over to flatten it to the bone further reduced tension. CONCLUSIONS AND CLINICAL RELEVANCE: Cerclage applied with a twist knot does not compress fracture fragments as effectively as cerclage applied with single loop or double loop techniques. Because greater compression of fragments will improve the stability of a fracture, a surgeon should strive to maximize the tension in the cerclage that they use. Experience and abilities of the surgeon are not associated with ability to tie cerclage wires tightly.     

Mechanical evaluation of pin and tension-band wire factors in an olecranon osteotomy model

OBJECTIVE: To evaluate the effect of altering pin and wire diameter, wire position and configuration, and osteotomy angle on applied load and absorbed strain energy in a pin and tension-band wire (PTBW) fixation model. STUDY DESIGN: In vitro mechanical study. SAMPLE POPULATION: Delrin models (n=96). METHODS: PTBW was applied to Delrin olecranon osteotomy models. A control configuration was defined and then altered, 1 variable (wire diameter, pin diameter, wire-hole position, wire configuration, osteotomy angle) at a time, to create 11 test configurations. Tensile force was applied and displacement at the caudal aspect of the osteotomy was measured. Fixation strength, in terms of tensile load and strain energy, was compared between control and each test configuration at 4 osteotomy displacements. RESULTS: Models with larger wire, pins, or combined figure-of-eight/lateral wires were stronger than control, whereas those with smaller wire, pins, or a solitary lateral wire were weaker. The superior strength of the larger wire was apparent for all assessed osteotomy displacement. CONCLUSIONS: PTBW fixation strength increases as implant diameter is increased, with wire diameter having greatest effect. Lateral wire configuration is weaker than figure-of-eight, but can be added to figure-of-eight configuration to increase strength. Wire-hole position and osteotomy angle have little effect on PTBW strength. CLINICAL RELEVANCE: Wire diameter is the key determinant of PTBW strength, whereas pin diameter is somewhat less critical. Wire passage through an additional hole proximally provides equivalent strength and may avoid soft-tissue entrapment and subsequent loosening.     

Multiple Intramedullary Wire Fixation of a Radial Fracture in a Dog

Multiple intramedullary wire fixation infrequently can be used as an alternative technique to plating, transfixation devices, single intramedullary pinning, or external coaptation for some radius and ulna fractures.
This report describes a comminuted fracture of the radius and ulna with fissures and comminution extending too far into the proximal radius for effective application of a bone plate or Kirschner-Ehmer apparatus. Resulting fracture instability and collapse prohibited effective use of external coaptation as a primary means of fixation. The radial fracture was repaired and stabilized with full cerclage wires and multiple intramedullary Kirschner wires. The dog was using the leg normally 12 months following surgery.     

Surgical repair of rib fractures in 14 neonatal foals: case selection, surgical technique and results

Reasons for performing study: Fractured ribs are encountered quite frequently in newborn Thoroughbred foals, often with fatal outcome. Surgical repair of fractures therefore requires consideration as a means of reducing mortality. Objectives: To evaluate the repair of rib fractures using internal fixation techniques in foals at 2 different equine hospitals following similar diagnostics and case selection. Methods: The records of 14 foals that underwent internal fixation of fracture ribs were reviewed. Subject details, clinical presentation, diagnosis, surgical technique, post operative care and complications were recorded. Follow-up information was obtained in 7 foals. Results: The fractured ribs were reduced and stabilised using reconstruction plate(s), self-tapping cortical screws and cerclage wire in 12 cases, Steinmann pins and cerclage wires in 1 case and both techniques in 1 case. Not every rib was reduced on each case. Surgical reduction was performed on an average of 2 ribs, range 1-3 ribs in each foal. At the time of writing, 4 foals had been sold, one age 2 years was in training and 2 others died from unrelated causes. Conclusions: Our data support the use of surgical stabilisation utilising reconstruction plates, self-tapping cortical screws and cerclage wire for selected cases of thoracic trauma in neonatal foals. The use of Steinmann pins may be suboptimal due to cyclic failure, implant migration and the potential for iatrogenic internal thoracic trauma. Potential relevance: Foals with existing extensive internal thoracic trauma resulting from rib fracture(s), or the potential for such trauma, previously considered to have a guarded to poor prognosis for survival, may be successfully managed with internal fixation of selected fracture sites.     

Clinical and Radiographic Evaluation of a Median Sternotomy Technique in the Dog

This study evaluated postoperative sequelae following a sternotomy closed with transsternal and parasternal sutures in nine dogs. Wound complications noted within 30 days suggested excessive intraoperative trauma to bone or surrounding soft tissues. Radiographic evaluation at the end of this period demonstrated a significant lack of osseous bridging between the sternal halves in eight of nine dogs. There was frequent wire breakage, suggesting instability of the sternal halves and considerable midline inaccuracy when splitting the sternum. Postoperative pain was minimal. This technique is suitable for use in dogs provided that swaged-on needles and sufficient transsternal wires are used, the sternebrae are carefully split on the midline, and the wires are carefully twisted to assure a tight closure.     

Mechanical comparison of median sternotomy closure in dogs using polydioxanone and wire sutures

Objectives : To compare the mechanical properties of two different materials for canine median sternotomy closure . Study Design : In vitro biomechanical study. Sample Population : Twelve canine cadaveric entire sternum and portion of associated ribs and musculature. Methods : Median sternotomy leaving the manubrium intact was closed using polydioxanone and stainless steel wire in a figure of eight pattern. Constructs were loaded in a servohydraulic material testing system and displacement was compared at loads of 125, 150, 200, 250, 300, 350 and 400 N, and at failure. Results : Displacement at loads up to 400 N and failure did not show any statistical difference between the polydioxanone and the stainless steel wire. However, the loading forces to create failure of the construct were superior for the stainless steel. Polydioxanone and stainless steel wire had the same response to distractive forces for loads applied up to 400 N. Clinical Significance : This study cannot recommend the use of polydioxanone over wires but suggests that polydioxanone can potentially be an alternative for primary median sternotomy closure in selected patients.     

X线电视在牛消化道疾病检查上的应用 Ⅰ.网胃与皱胃的正常X线影像特征

为了掌握健康牛网胃、皱胃的运动规律及其Ｘ线影像特征，运用日本带广畜产大学的大型Ｘ线诊疗车对该校８０头乳牛的网胃和皱胃运动进行了长期观察。结果发现，由于网胃的网格里有沙粒、细石和金属异物等存在，使网胃的影像清晰可见。网胃的运动为两相收缩，即从运动休止状态开始沿着膈的方向进行第一阶段的收缩，稍为停顿后，再继续第二阶段强有力的收缩。皱胃底部常沉积有一定量的泥沙以及金属异物等，使得皱胃更易被辨认。     

Comparison of Three Methods of Ulnar Fixation in Horses

Objective- This study compares the mechanical properties of three methods of equine ulnar fixation: dynamic compression plating, pins and wires tension band, and a prototype grip system.
Study Design- The mechanical properties of dynamic compression plating, pins and wires tension band, and a prototype grip system repair of equine ulnar fractures were evaluated in a cadaveric osteotomy model.
Animals or Sample Population- Fifteen pairs of the radius and ulna from equine cadavers.
Methods- The three repair techniques were evaluated to mimic the pull of the triceps brachii muscle in single cycle to failure and in cyclic fatigue loading. Single cycle results were evaluated as the axial and angular displacement. Cyclic fatigue results were evaluated as the number of cycles to failure.
Results- Dynamic compression plate fixation and pins and wires tension band had significantly less axial displacement of the proximal fragment than the grip system ( P <.05). No significant difference in angular rotation of the proximal fragment was present between the three techniques. Dynamic compression plating had significantly greater fatigue resistance than the grip system ( P <.05). Cyclic failure was characterized by screw loosening or breakage and wire breakage.
Conclusions- Dynamic compression plates were better than the other techniques at maintaining compression of a transverse ulnar osteotomy at the level of the anconeal process just proximal to the trochlear notch.
Clinical Relevance- Knowledge of fixation technique mechanical properties is essential for surgeons to select the proper method of fracture repair.     

Biomechanical comparison of a circular external skeletal fixator construct to pin and tension band wire fixation for the stabilization of olecranon osteotomies in dogs: a cadaveric study

OBJECTIVE: To compare anatomic reduction and the biomechanical properties of a circular external skeletal fixator (CESF) construct to pin and tension band wire (PTBW) fixation for the stabilization of olecranon osteotomies in dogs. STUDY DESIGN: Cadaveric study. ANIMALS: Forelimbs from 12 skeletally mature mixed-breed dogs, weighing 23 to 28 kg. METHODS: An olecranon osteotomy was stabilized with either a CESF construct or PTBW fixation. A single distractive load to failure was applied to each specimen through the triceps tendon. Osteotomy reduction and biomechanical properties were compared between fixation groups. RESULTS: Reduction was not significantly different (gap: P =.171; malalignment: P =.558) between fixation groups. Osteotomies stabilized with the CESF had greater stiffness (P <.0001) and maximum load sustained (P <.0001) compared to PTBW fixation. There was no significant difference for yield load (P =.318) or for load at 1 mm of axial displacement (P =.997) between fixation groups. Failure of fixation occurred by bending of the intramedullary Steinmann pin and the fixation wires in the CESF specimens and by untwisting of the tension band wire knot with pullout and bending of the Kirschner wires in the PTBW specimens. CONCLUSIONS: Specimens stabilized with the CESF construct had similar reduction and yield load, greater stiffness and maximum load sustained, and less elastic deformation than specimens stabilized with PTBW fixation. CLINICAL RELEVANCE: The CESF construct may provide a biomechanically favorable alternative to PTBW fixation for stabilization of olecranon osteotomies in dogs, and its application warrants clinical investigation.